Conveyor belt systems use a moving conveyor belt for transporting sand, gravel, coal and other bulk materials from one location to another location. Sometimes a residue of the bulk material still sticks to the conveyor belt when the bulk material falls from the conveyor belt at the end at a deflection roller. A conveyor belt scraping device of the type discussed serves the purpose of scraping off the residual bulk material that clings to the conveyor belt.
A first conveyor belt scraping device is normally situated directly at the deflection roller of the conveyor belt as a so-called primary scraper. A secondary scraper is also situated in the majority of cases on the lower run of the conveyor belt behind the primary scraper in the running direction of the conveyor belt.
The scraping segments of a conveyor belt scraping device, which in the majority of cases are arranged in a plurality side by side, are fastened so as to be replaceable on a support shaft which, in the majority of cases, is rotatable and frequently also additionally linearly adjustable and extends transversely with respect to the conveyor belt.
A tensioning device is connected to one end of the support shaft or connected to both ends of the support shaft and comprises a lever structure or pretensioned springs in order to generate the necessary pretension. Occasionally a tensioning device also comprises a drive motor. The drive motor is then actuated by an electric or electronic control means.
When just one drive motor is discussed in the present case, this then includes a variant where several drive motors are provided, in particular one drive motor on each end of the support shaft.
When a drive motor is discussed in the present application, this then always means the drive motor as such including the output element of the drive motor, for example a rotating output shaft or a linearly extendable and retractable output element. Said output element is relatively movable in relation to the body of the drive motor and moves, in turn, a drive element for the scraping segment.
The drive motor is arranged in a stationary manner, for example on a stationary mounting, on which the support shaft is also rotatably mounted, or for example on a frame structure of the conveyor belt system overall.
The drive motor applies a rotatingly or linearly acting pretension force onto the support shaft which, in turn, moves the scraping segments to abut against the conveyor belt at a desired pretension with their scraping ends. The pretension has to be high enough in order to scrape off any bulk material residues clinging to the conveyor belt in a reliable manner, however it must not be so high that the conveyor belt is damaged.
During operation, proceeding from the scraping end, the scraping segment is subject to wear as it is situated in grinding engagement with the continuously moving conveyor belt.
In the case of a known conveyor belt scraping device (DE 60 2004 005 771 T2), the drive motor is controlled in a comprehensive manner. More precisely, two drive motors are present here, namely a first preferably pneumatic drive motor which only brings about the rotation of the support shaft, and a second electric drive motor which is realized as a linear motor and pivots the unit, produced from the first drive motor and the support shaft, about a stationary pivot axis in a circular-arc manner toward the conveyor belt or away from the conveyor belt. In the case of said design, only the second drive motor is arranged in a stationary manner. The state of the scraping segment is monitored by a wealth of sensors (torque sensor, load detection sensor, temperature sensor, wear sensor) and, by actuating the two series-connected drive motors, the scraping end of the scraping segment is pressed onto the conveyor belt always at the correct pressing force, that is to say pretensioned in relation to the conveyor belt.
The scraping segment can also be completely released from the conveyor belt and pivoted well away, for example in order to replace the worn scraping segment, as a result of actuating the drive motors, in particular the second electric drive motor which is realized as a linear drive.
Even when the singular is used when referring to the scraping segment, everything also applies to the plural. In particular, in practice it is normal to have several scraping segments mounted side by side in a row or offset with respect to one another on the support shaft over the width of a conveyor belt.
The previously explained, disclosed conveyor belt scraping device can hardly be improved with regard to the control of the pretension of the scraping segments. However, the expenditure involved here on drive technology, measurement technology and control technology is very high. The disclosed conveyor belt scraping device is therefore too expensive for many applications.
There is already known a conveyor belt scraping device which allows for reliable pretensioning of the scraping segments (EP 0 566 486 A1). Here a manual coupling is arranged between the drive element of the drive motor on the one side and the support shaft on the other side. This creates the necessary degree of freedom in order to adjust the relative rotational position of the support shaft and of the drive element manually with respect to one another. In the respectively manually adjusted position, the relative position of the support shaft and of the drive element of the drive motor can be fixed with the manual coupling.
The characteristic of this tensioning device consists in that the pretensioning of the scraping segment in relation to the conveyor belt can be performed manually with the drive motor in an end position. With every drive movement of the drive motor, for example out of a position in which the scraping segment is completely pivoted away (released) from the conveyor belt, the scraping segment can be placed against the conveyor belt again at the desired pretension as a result of approaching the end position of the drive motor. An adjustment of the pretension or a readjustment on account of wear on the scraping segments can be effected in the case of said design by releasing the manual coupling and manually adjusting the support shaft in relation to the drive element or the drive element in relation to the support shaft.
Finally, a manual coupling takes the place here of the first drive motor in the prior art mentioned above. As a result, the expenditure on drive technology, measurement technology and control technology for this conveyor belt scraping device is clearly less than before.
A manual coupling is operated by hand, but it can be effected with a tool, for example a screwdriver. Particularly preferred, however, is that the manual coupling is actuatable as such by hand without a tool.
The drive motor can be realized in any manner in this prior art. It is possible, in particular, to use a hydraulic drive motor or a pneumatic drive motor. It is also disclosed to use an electric drive motor.
All things are also possible, in principle, as regards the design of the drive motor. For example, it can be a drive motor where an output shaft is rotatingly moved. The rotational movement thereof can then be transmitted to the support shaft by means of a step-up gear unit or, preferably, a reduction gear unit.
A problem with above extensively explained construction of the prior art is that during operation of the conveyor belt scraping device the wear on the scraping segments leads to a decreasing pretension of the scraping segments at the conveyor belt.
Examples in the present disclosure improve the prior art method of operating a conveyor belt scraping device in that decreasing pretension in case of wear on the scraping segments can be compensated for.
Presumption for realizing the teaching of examples disclosed herein is the use of an electric drive motor. The design as a linear drive motor can be particularly preferred.
According to certain examples disclosed herein the force of the electric drive motor necessary for a desired pretension of the scraping end of the scraping segment against the conveyor belt is determined and regulated by means of the control means via the current drawn from the electric motor. A particular motor current is said as a boundary value for the desired pretension of the scraping end of the scraping segment. And then the electric drive motor is driven again and again at predetermined or determinable time intervals against the conveyor belt, in each case until the motor current said as a boundary value for the desired pretension is reached. Thus decreasing pretension following wear on the scraping segments can be comfortably compensated for.
Here, the advantages of manual adjustability are combined with the advantage of electric regulation of the drive motor.
Particularly preferred with regard to the manual adjustment is the adjusting of the relative rotational position as a result of manually rotating the support shaft with the position of the drive element unchanged. The support shaft can be rotated, for example, using a torque wrench until the desired pretension of the scraping segments is achieved. The manual coupling can then be engaged again such that said relative position of the drive element in relation to the support shaft is fixed.
Particularly advantageous, in this case, is that the manual coupling is connected to the support shaft in a non-rotatable manner and to the drive element in a manually adjustable and fixable manner. In addition, particularly advantageous is a design of the coupling in such a manner that the connection between the coupling and the drive element comprises a detent mechanism which is adjustable in steps and a stepless precision adjusting mechanism. Such a combination allows for rapid rough adjustment as a result of simply selecting a new notch, but also allows for a precision adjustment which is then subsequently effected in a stepless manner. The precision adjustment expediently takes place by way of corresponding adjusting screws.
There is naturally a wealth of possibilities for the arrangement of the drive element. The realization of the drive element as a gear wheel of a reduction gear unit has already been named above as an example. Structurally, it has proven particularly expedient for the drive element to be a lever which is mounted so as to be freely rotatable on the support shaft. In principle, the drive element can also be integrated in the output element of the drive motor.
The design with the freely rotatably mounted lever as the drive element obtains further importance in the overall arrangement where the mounting comprises a main carrier with a first end and a second end. The first end is the top end where the main carrier is in a vertical arrangement and the second end is the bottom end. The support shaft is expediently mounted in the main carrier by means of the holding bearing on the second end. The drive element, realized as a lever, protrudes laterally from the main carrier on the second end. An angular arrangement is consequently created which allows the drive motor to be mounted between the first end of the main carrier and the free end of the drive element. The entire arrangement is consequently in the form of a triangle. This is very expedient as the structure is able to be mounted quickly on the conveyor belt system by mounting the main carrier with the attachment parts.
The method according to the examples disclosed herein is more particularly easy to apply if the drive motor comprises two end positions, namely a first end position in the placing direction and a second end position in the releasing direction, wherein, for placing the scraping end of the scraping segment against the conveyor belt, the drive motor is moved into its first end position, and with the drive motor in the first end position, the scraping segment is placed with its scraping end against the conveyor belt at the desired pretension as a result of the application of force on the support shaft by utilizing the manual coupling and is fixed in the adjusted position by means of the manual coupling.
The afore-described design works without specific sensors.